It is common in certain types of air-bag for there to be both inflatable and non-inflatable regions. For example, FIG. 1 shows a schematic view of a conventional inflatable curtain (IC) type air-bag. Prior to inflation, an air-bag of this kind is typically stored in a rolled and/or folded fashion along the roofline of the vehicle, above the side windows. When the air-bag is activated (if, for instance, a roll-over situation is detected), the air-bag is inflated and unrolls downwardly to cover the front and rear side windows, as well as the B-pillar. This provides cushioning if a vehicle occupant is thrown against the internal side wall of the vehicle, and also presents a barrier which helps to prevent the occupant from being thrown out of the vehicle through the window.
Referring to FIG. 1, the air-bag 1 comprises a number of inflatable regions, including a main gas delivery passage 2 which runs along an upper edge of the air-bag 1, and a series of inflatable cells 3 which are generally parallel with each other and in communication at one end with the main gas delivery passage. A first group 4 of the inflatable cells 3 is, after deployment, aligned with the vehicle's front side window, and a second group 5 of the inflatable cells 3 is aligned with the vehicle's rear side window.
Between the first and second groups 4, 5 of inflatable cells 3 lies a non-inflatable region 6 of the air-bag 1, which is generally aligned with the vehicle's B-pillar.
An air-bag of this type is typically formed in a one-piece woven (OPW) construction, in which two superimposed layers of fabric are woven simultaneously on a loom. In selected regions, the layers are interwoven with one another, as is known in the art. To form the inflatable regions 2, 3, the two layers are not interwoven with each other. A space is therefore formed between the layers, into which gas may be introduced to inflate the inflatable regions 2, 3.
In regions immediately surrounding the inflatable regions 2, 3, the layers are strongly interwoven to form substantially gas-tight boundaries for the inflatable regions 2, 3. Referring to FIG. 1, interwoven regions 7 of this type are formed around the gas delivery passage 2, and around the inflatable cells 3. These interwoven regions 7 must be mechanically robust, as substantial forces will be placed on them as the inflatable regions 2, 3 are inflated during rapid deployment of the air-bag 1, and also if a vehicle occupant is thrown against the air-bag 1 during an accident situation.
The two layers from which the air-bag 1 is formed will typically comprise fabric layers, formed from interwoven warp and weft yarns. The warp yarns are substantially perpendicular to the weft yarns. In an uninterrupted region of each layer, each warp yarn may pass alternately under and over each weft yarn that is encountered along its length. Similarly, each weft yarn may pass alternately under and over each warp yarn that is encountered along its length. In alternative weaving patterns, such as a “herringbone” pattern, a yarn of one type may pass under or over two or more consecutive yarns of the other type that are encountered along its length. The skilled person will understand that different suitable weave types may be used.
In interwoven regions, some of the warp and/or weft yarns that form one or both layers pass across to the other layer, and are interwoven with the yarns of the other layer, thus forming connections between the two layers.
Since the interwoven regions 7 that bound the inflatable regions 2, 3 must be strong and reliable, a large proportion of the yarns of the two layers are involved in connections between the two layers in these regions 7. For example, 100% of the yarns in these regions 7 may be involved in interconnections between the layers. The non-inflatable region 6 is bounded by interwoven regions 7, and is not connected to any of the inflatable regions 2, 3. There is therefore no requirement for the two layers of the air-bag 1 to be tightly interwoven in the non-inflatable region 6. It is also desirable for the non-inflatable region 6 to have a low stiffness, to assist in ease of rolling the air-bag 1 when installing the air-bag 1 in a vehicle.